Manufacture of incandescent lamps



1,647,139 Nova 1 2 c. F. LORENZ MANUFACTURE OF INCANDESCENT LAMPS Filed June 25. 1922 INVENTOR CHARLES E LORENZ AT TORNEY useful life and its burn-out life.

much as these terms are peculiar to the 1n- Patented Nov. 1, 1927.

UNITED STATES.

PATENT OFFICE.

cnAnLns rannnmox LonnNz, ornAsr ORANGE, NEW nnsn'v, ASSIGNOR 'ro WEST- INGHOUSE L MP COMPANY, A conroRA'rIoN or PENNSYLVANIA.

MANUFACTURE OF INCANDESGENT LAMPS.

Application filed June 23,1922; Serial No. 570,484.

My invention relates to a method of bringing the useful life and burn-out l fe of electric incandescent lamps into close rela-.

tion and relates particularly to filaments for such lam s.

An ob ect of the invention is to provide a filament of such character that its life will be automatically terminated when it reaches a point at which an operation of the lamp is uneconomical.

Another objectof the invention is-to provide a lamp in which the mean lumens per watt during the life of the lamp are substantially constant.-

Other objects of my invention .will be apparent from a .reading of the following specification. A

It is customary in the art of lncandescent lamp manufacture, when speaking of the life of a lamp, to distinguish betweeii its nas-' candescen't lamp parlance, and will be frequently used in this a plicatlon, it may be well to define them. T e burn-out life refers to the number of hours of burning'of the lamp until a failure of the filament occurs by breaka e or otherwise. The useful life of a lamp lndicates the number of hours during which it is economical to burn the lamp. Inasmuch as an incandescent lamp decreases in efliciency as it burns, it is obvious that when a lamp has fallen in efficiency beyond a certain point it is more economical to replace it with a new lamp than it is continue burningthe lamp at lower eflic1enc This economical limit of operation mar s the end of the useful life of the lam In practice, however, most incan escent lamps are used throughout the burn-out life due to a mistaken idea of economy on the part of many users, partly by reason of their inability to determine the economlcal llmzt in the life of the lamp. 7

There is a comparatively wide margin between the useful and the burn-out life of the lamp which in some types of of lamps amounts to 100% of use 111 life. margin represents waste, and, therefore, should be avoided.

By reason of the peculiar form of filament employed in my invention, this waste margin may be eliminated and the present standard for the useful life of a lamp is main- This.

tained and it has been found in practice that the mean lumens per watt throughout the useful life have been slightly increased. In other words, by reason of my improved filament, a lamp is produced which tends to bring the burn-out life and the useful life into coincidence, while at the same time a lamp is provided which has a useful life equal or slightly better than that of the present standard.

It is well known that one of the elements.

upon which the life of a lamp depends is the time .taken by the filament to disintegrate by vaporization. It is also known that the life of filaments varies dependin upon the ratio of the surface area tot e volume. Thus a relatively small diameter filament as found in a lamp, for example of 30 watts, 110 volts, will have a useful life of a given number of hours and will continue to burn for an additional amount of time with a gradual decrease in efficiency. The filament of a 30 watt lamp will, however, burn out very near the end of its useful life, whereas, the filament of a 60 watt lamp will continue to burn for a considerable period after its useful life has ended. The reason for this difference in the burn-out life of the two lamps resides in the fact that the surface area of the smaller filament as compared to its volume is great enough to cause a burnout due to vaporization in an interval of time that is very nearly equal the useful life of the filament.

It will-be understood that the filament of V a 60 watt 110 volt lamp is'essentially of a greater diameter than that of a 30 watt equal to 7rd it follows that the surface area per unit of length of a larger diameter filament will be relatively small whereas the small diameter filament will have a comparatively large surface and small volume per unit of length. In the 30 watt lamp this condition more nearly approaches the ideal in which the useful life of the lamp terminates at about the sametime that the filament gives out. I

Therefore, for the urpose of benefiting by the advantage game; by the relatively large surface of a small diameter filament I employ, as a light source, a plurality of small filaments preferably entwined or twisted together. A filament may thus be provided for use in a lamp of a comparatively high wattage capable of giving the standard amount of useful life but having its useful life and burn-out life close together, and a lamp may be produced having the advantage of the useful and burn-out life of substantially equal lengths as obtained in a lamp of relatively low wattage.

As an example, it will be understood that a 60 watt, 115 volt lamp will not burn out until its candle power has dropped to an objectionably great extent; that is, the burnout life of the lamp will be considerably greater than its useful life. When racticing my invention to produce a lamp 0% approximately 60 watts. 110 volts, I employ two filaments of about the diameter used in a 30 watt, 110 volt lamp. It has been fund preferable to twist these filaments together and thereby produce a continuous member similar to a cord or rope which may be. draped over the supports of a lamp stem in a manner similar to that employed for the mounting of the ordinary single wire filament. Owing to the fact that portions of the twisted wire make contact with each other, it may be desirable to slightly increase the diameter of the twisted wires to compensate for radiation lost by the contacting portions in order to maintain the illuminating value.

It will be evident that lamps of other watta e may be produced with the same desira le result, for instance, in a 100 watt lamp,

three filaments may be twisted together, each of the said filaments being of a diameter as used in a 33 watt lamp. Thus a relatively large surface area per unit of length or volume of filament will be produced as compared with the surface per unit of length of volume of a single round filament of the same current rating. The total filament surface in the present invention and as heretofore employed are obviously the same.

The invention will be more fully understood by reference'to theac'companying drawing in which Fig. 1 shows azig-zag type of filament composed of a stran of heavy wire and a strand of relatively fine wire associated therewith Fig. 2 is an enlarged view of a portion of the filament shown in Fig. 1; Fig. 3 is a view showing a section taken on line III-III in Fig 2; Fig. '1- is a view of a. portion of a modified form of filament showmgthe strands thereof separated by spacer members to hold the strands apart and Fig. 5 is a view showing a. section taken on line V-V in Fig. 4. a

A preferred embodiment of the invention as shown in drawing may include a filament 10 of relatively small cross sectional area entwined or otherwise associated with a filament 11 of a relatively large cross sectional area to produce a filamentary body or the portion of the langer filament between the connectors at each side of the break will become over-loaded and in a short time will also break terminating the life of the lamp.

A filament of relatively small diameter when employed for the purpose as above described, may, altho'ughacting as a parasite, serve as a controlling member of the filamentar body. It will therefore be understood t at by the addition of a filament in which the burn-out life and the useful life are more near the'ideal condition, a lamp of any given wattage may be regulated to have its life terminated with that of the parasitic or auxiliary filament.

It will be evident that an auxiliary filament of anyconfiguration in cross section may be em loyed. It has been found that filaments 0 different outline in transverse cross section have different life characteristics and a filament of a certain configuration may be produced which will burn out in a given length of time. For example, a flat filament may be employed as the controlling or relatively small filament in conjunction with a relatively large filament, as, for example, that indicated by the numeral 11, to serve as the controlling element to terminate the life of the larger filament. Such fiat filament may be twisted or wound about another filament of larger transverse cross sectional area.

Inasmuch as a filament produced in accordance with my invention has the required light source area with a relativel small increase in the weight per unit 0 length of filamentary material and, furthermore, as the filament for a lamp of given wattage and voltage will necessarily be shorter than commonly employed,-it will be appreciated that a saving of said material results.

It will be evident that a stranded filament giving the desired luminosity is an advantage inasmuch as the increased flexibility reduces breakage of the filament during handling in manufacture, or subsequent transportation.

My invention therefore not only contemplates the use of a light source comprising a plurality of filaments of such relative proportions that when in operation within the lamp they mrve to bring the useful life of the lamp more nearly coincident with the burnout life, but also provides a more rugged lamp thus increasing its value to -out life of an electric incandescent lamp which consists in proportioning the ratio between the volume and the surface area of the light source by. entwining a plurality offilaments to'constitute a filamentary body and in selecting filaments of such size and numher as to produce disintegration and failure of the several filaments at the termination of their useful life.

2. The method of" controlling the burnout life of an incandescent electric lamp which consists in associating a filament of relatively large diameter with a filament of relatively small diameter to cause an overloading of a portion of one of the filaments upon a failure of another.

- 3. A filame'nt'for an incandescent electric lamp comprising a plurality of strands of different cross-sectional areas twisted together to constitute an integral filamentary body. q

4. A filament for an incandescent electric o lamp comprising a plurality of strands ofdiflerent cross-sectional areas.

.5. A composite filamentary body com posed ofa plurality of strands, one being of relatively small transverse cross sectional area whereby the failure of said small strand will accelerate the failure of the remainder."

6. A filament for an incandescent electric lamp comprising a plurality of" entwined v strands having diflerent life characteristics to eflect a failure ofone filament upon the failure of another. l A

In testimony whereof, I. have hereunto subscribed'my name this 22nd day of June, 1922.

CHARLES FREDERICK LORENZ. 

